Nonsmoke-back solid fuel furnace



June 17, 1952 D. T. CAMPBELL 2,600,614

NONSMOKE-BACK SOLID FUEL FURNACE Filed Feb. 24. 1949 2 SHEETS-SHEET l N IN VEN TOR.

' ZZqI/Ja T. (391mm,

June 17, 1952 D. 1-. CAMPBELL NONSMOKE-BACK SOLID FUEL FURNACE 2 SHEETS-SHEET 2 Filed Feb. 24, 1949 a EL INVEN TOR. 121W; 21 621212 125221: BY.

W6 ATTORNEY Patented June 17, 1952 UNITED STATES PATENT OFFICE NONSMOKE-BACK SOLID FUEL FURNACE David '1. Campbell, Indianapolis, Ind.

Application February 24, 1949, Serial No. 78,193

4 Claims. 1

The present invention relates to a solid fuel stoker and its primary objects are to overcome certain disadvantages in stokers as heretofore produced and used. Thisapplication is a continuation-in-part of my copending application Serial No. 38,015, filed July 10, 1948, for Non- Smoke-Back Solid Fuel Stoker, now abandoned.

One of the problems encountered in the use of previously known stoker structures is known as smoke back, which may be described as the tendency of mechanically fed solid fuel burners to discharge smoke through the fuel feed mechanism when air is supplied to the burner at a time when the conveyor through which fuel is intended to be supplied to the combustion chamber is empty, or only partially filled with fuel. The present invention provides means for preventing the flow of smoke from the combustion chamber back through the fuel feed conduit regardless of the condition of that conduit. One principal factor in thus preventing smoke-back lies, in the disclosed embodiment of my invention, in the fact that I provide means associated with the source of air supply and so arranged that, under normal conditions of stoker operation, a cushion of air will be maintained in the fuel feed conduit at a point and at a pressure value such as to block any possible fluid flow from the furnace combustion chamber toward any opening in such conduit; and that, under abnormal conditions, such as depletion or exhaustion of the fuel in the conduit between the source of fuel supply and the point at which such cushion is normally maintained, the supply of combustion-supporting and pressure-raising air to the combustion chamber will be almost completely discontinued by the diversion of substantially the entire volume of air supplied from such source to be discharged to the atmosphere.

It is a further object of the invention to provide a. simple arrangement of mechanism of such character that the above-described functions will be carried out automatically and without the intervention of an operator or attendant and even without the intervention of control devices or mechanisms.

It is, of course, desirable for many reasons, to obviate the necessity for hand feeding a solid fuel stoker. Every commercial stoker with which I am familiar provides .a hopper which must be hand fed from the bin, coal room, or other reservoir for fuel. True, bin-fed stokersare known; but so far as I am advised,

every bin-fed stoker commercially known before my present invention, is a custom built job, based upon a production unit which includes a hopper, and produced by removing the hopper from the assembly and adding to the assembly some improvised conveyor means for conducting fuel from the customers bin to the conveyor, forming a part of the production unit, and originally intended to feed fuel from the standard hopper to the combustion chamber. As a consequence, a bin-fed installation is almost prohibitively expensive, involving substantial amounts of labor, and individual design. A further object of my invention, then, is to provide a standard production stoker unit basically designed to be fed from a bin or storage room.

A further object of the invention, then, is to provide an organization of the character described which may readily be converted to a hopper type of stoker.

Still further objects of the invention will appear as the description proceeds.

To the accomplishment of the above and related objects, my invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that change may be made in the specific construction illustrated and described, so long as the scope of the appended claims is not violated.

Fig. 1 is a perspective view of my improved stoker shown in operative association with a solid fuel burner and a coal room, illustrated more or less diagrammatically;

Fig. 2 is a side elevation, upon an enlarged scale, showing fragments of the conveyors and the air delivery conduit, and illustrating the transfer box, the blower, the prime mover, the drive trains, and the conduit for maintaining superatmospheric pressure in the transfer box, parts being broken away for clarity of illustration;

Fig. 3 is a transverse section taken adjacent the front end of the transfer box, and showing the air scoop in its relation to the blower;

Fig. 4 is a fragmentary horizontal section, showing the coacting portions of the two conveyors, and the transfer box, taken substantially on the line 4-4 of Fig. 3; and

Fig. 5 is a section taken substantially on the line 55 of Fig. 3 and further showing the re lation between the air scoop and the blower.

Referring more particularly to the drawings, it will be seen that I have illustrated more or less diagrammatically a standard solid fuel burner l0 including a smoke vent ID, a firepot II and an air delivery box l2, all of these parts being of any suitable standard construction. The burner I is positioned generally adjacent a coal room indicated at I3 and partially defined by a wall 14. A screw conveyor indicated generally by the reference numeral i5 is mounted to penetrate the wall 14 and comprises a conduit [6 in which is operatively journalled a screw H carried on a shaft I8. As illustrated, one end of the shaft [8 is journalled in a suitable bracket l9 mounted within the coal room l3, at least a portion of the conduit 16 disposed in said coal room being open to provide access of the screw H to the fuel supply maintained in the room l3.

I'he opposite end of the conduit i6 is secured to a transfer box or housing 20 in registry with a suitable port therein, and the shaft l8 extends into and through the chamber 2| defined by the housing 20. A sprocket 22, or other powerreceiving means, is mounted upon that portion of the shaft [8 which projects beyond the housing 20. If the conveyors are mounted, as shown, substantially in a common horizontal plane, a short screw section 23, whose pitch is opposite the pitch of the. screw U, will preferably be mounted on the shaft 3 within the chamber 2|, to assist in moving fuel, delivered to the chamber 2| by the screw l1, laterally away from the axis of the shaft I8. Where relatively soft fuels are to be, handled, however, the shaft I8 will enter the chamber 2| at a level above the level of exit therefrom of the screw 26, presently to be described, so that the fuel will fall by gravity into the zone of influence of said screw and in such an arrangement, the screw sec- 5 tion 23, may be omitted, thereby reducing the tendency of the fuel transferring means to crush and shatter the fuel being handled.

A second conveyor, indicated generally by the reference numeral 24, comprises a conduit 25, one end of which is arranged to deliver fuel to the firepot II and the other end of which is secured to the housing 20 in registering association with a suitable port therein. The screw 25 is arranged within the conduit 25 andv traverses the chamber 2!, the shaft bearing said screw projecting beyond the housing and carrying outside the housing. 20, a sprocket 27 or other suitable power-receiving means. It will be obvious that, fuel, delivered tow the chamber 2! by the screw I], will move through the chamber 2| and will be picked up by the screw 26 and carried through the conduit 2-5 for delivery to the firepot IL It will be noted that the axes of the screws 11 and 26 are substantially parallel and located very close to each other, whereby crushing and shattering of the fuel is further minimized.

Upon a suitable standard 28, I support a motor 29 whose spindle is directly connected to drive the shaft 30 of the blower 3|. Conduit means 32 connects theoutlet of the blower 3| with the air box l2 of the burner Iil. According to standard practice, the blower 31 is a squirrel cage type blower which delivers substantial volumes of air at relatively low static pressures. The dynamic, or flow, pressure produced by the operation of such a blower is, as is well known, of substantial amount.

Penetrating a wall of the conduit means 32 directly at the mouth of said conduit means is a fitting 33, said fitting inclining outwardly away from theblow'erport 44. in the'manner perhaps most clearly illustrated in Fig. 5. The inlet end of said fitting 33 spans more than one-half of the vertical height of the blower port 44 and conduit means 32, as is shown in Fig. 5, and spans substantially the entire axial width of the blower rotor 46, as is shown in Fig. 3. I presently believe that, for the accomplishment of the intended functions of my invention to an optimum degree, the effective area of the mouth 55 of the fitting 33, shown herein as being approximately one-half the effective area of the conduit means 32, must be at least one-third the area of the blower outlet and the said conduit means 32. Thus, the mouth 35 of the fitting 33 is so designed and arranged as to be capable, under suitable conditions, (as when one of the conveyors [5 or 24 runs empty, as described hereinafter) of receiving and passing substantially the entire volume of air delivered by the rotor 46 at any given moment. It is also so designed and arranged as to mask a substantial part of the conduit means 32 and to be subjected to the maximum flow pressure produced by operation of the blower 3], so that the static pressure within the fitting 33 and within closed or substantially closed spaces communicating therewith, will exceed any static pressure which the blower is capable of producing or maintaining within the combustion chamber of the burner it, which is, of course, of relatively large volume, and which is vented through the usual stack. A conduit 35 which, in the illustrated embodiment of the invention, is a flexible tube, connects the fitting 33 with the interior of the chamber 2|. Preferably, as shown particularlyv in Figs. 2 and 3, the conduit 35 will enter said chamber through a port 41 located substantially on the longitudinal center line of the transfer box 20, midway between the axes of the screws ll and 26, and near that end of the box into which opens the tube 25.

I presently believe that the introduction of the scoop 33 into the blower outlet at the point of maximum wheel pressure results in what may be termed a diversion of such wheel pressure. That is, it is well understood that, in normal operation of such a blower as that illustrated herein, static pressure at the blower outlet will be a maximum at the point at which the, rotor blades finish their traversal of the outlet and start to reenter the arcuate passage of the housing; andthat that pressure progressively decreases across the outlet. The scoop 33, located and, proportioned as it is, thus receives maximum wheel pressure and, because of the restrictions to flow created by the screws and; the coal in the conveyors l5, and 24, substantially that maximum wheel pressure is built up in the conduit 35 and the transfer box 20. Some of the air delivered by the blower will flow through the passage 32, while some of the airdeliveredby the blower will flow through the scoop 33.; and conduit 35; and pressure conditions currently existing in said scoop. and conduit will; affect the proportionate now through the two paths. Since air flowing through passage 32. must flow beneath the lower edge of themouth 45 of the scoop 33, it will, ofcourse, be at a lower pressure, since its path is thus substantiallyremoved from theregion of maximum wheel pressurewithin the blower outlet.

Particularly in regions where soft, highly frangible coal is prevalent, difficulty is experienced in transferring fuel from one screw conveyor to another through a transfer box; and I minimize that diflicultyby mounting. myscrews l1. and 26 with. theiraxes closely. adjacent each clogging of the fuel.

Also, where such fuels are widely used, any substantial flow of air through the conveyor which communicates with the furnace combustion chamber must be avoided. This is for the reason that, if air in substantial volume flows over or through the fuel in the tube 25, combustion or coking of the fuel may be initiated in the tube itself by conduction of heat from the combustion chamber along the column of fuel in said tube, and because of the low melting and ignition points of such fuels. So long as the tube 25 is substantially filled with fuel, the resistance of such column of fuel therein will be sufiicient to prevent the flow of any substantial volume of air through said tube from the chamber 2i since the pressure differential between the chamber 2I and the combustion chamber is relatively slight.

A belt or chain 36 transfers power from a pulley or sprocket 29' mounted on the spindle of the motor 29 to a pulley or sprocket 31 mounted on the inlet shaft of a reducer unit 38. A shaft 39, connected to the outlet shaft of said unit 38, carries a sprocket 40 which is connected, by a chain 4|, with the sprocket 21 of the conveyor 24; and further carries a sprocket 42 connected by a chain 43 with the sprocket 22 of the conveyor I5. Thus, it will be seen that the screws of the two conveyors are driven, through short power transmission trains, separately from the motor 29. No problems of whip or twist thus exist in the organization. Additionally, the conveyor unit I5 may readily be removed from the organization, and a hopper may readily be associated with the transfer box 2|] to deliver coal to the chamber 2|, whence it will be picked up by the conveyor 24 and delivered to the burner I0. Alternatively, a short conveyor fed from a hopper may be substituted for the conveyor I5 and similarly connected to the transfer box 20.

Because of the connection 33, 35, 41, a superatmospheric pressure, proportionate to the static and dynamic pressures produced by the blower 3 I, will normally be maintained in the chamber 2I. The pitch of the screw 26 is faster than the pitch of the screw I! in order to guard against clogging of fuel in the chamber 2 I. Alternatively, the screw 26 may be driven faster than the screw I! for the same purpose. As a consequence, it sometimes happen that the conveyor 24 will be emptied, or partially emptied. There always exists, also, the possibility of exhaustion of the coal supply in the room I3; or the possibility of failure of the conveyor I5 because of arching or other difficulties in the coal room I3. With standard stoker constructions, emptying or partial emptying of the fuel-delivery conveyor will almost invariably result in a flow of smoke from the combustion chamber through the conveyor corresponding to the conveyor 24, and the discharge of smoke into the house, whenever the blower operates while the fuel-delivery conveyor is empty or partially empty, since such a situation, in the usual stoker installation, leaves an open passage through the fuel-delivery conduit for the escape of gases from the combustion chamber in which a slightly superatmospheric pressure is maintainedby the air-supply mechanism.

.' As suggested above, in my installation, on the other hand, there exists at all times an unre stricted passage for air flow from the blower 3I to the chamber 2 I. Air flowing from the blower to the combustion chamber must pass through the fire bed in the furnace, whereby its free flow is restricted, Therefore, if the tube 25 should run empty or substantially empty, the major portion of the air volume thrown by the blower 3I will flow through the fitting 33 and conduit 35 to the transfer box 20, and thence through the relatively unimpeded path through the tube 25 to the fire box. Gases cannot, of course, flow against this stream from the combustion chamber toward the transfer box 20.

If, onthe other hand, the tube It should, for any reason, run empty or substantially so, smoke bac will be prevented by the fact that the disclosed organization will, under such circumstances, rob the combustion chamber of substantially all its air supply, whereby the static pressure in said combustion chamber will drop substantially to atmospheric value. As is stated above, the fuel bed in the combustion chamber imposes a barrier to air flow therethrough, which can be overcome only by a substantial superatmospheric pressure in the air box I2. The tube I6 beingempty, or substantially so, and the fitting 33 being proportioned and designed as described above, there is provided an unrestricted flow passage from the blower exhaust to the atmosphere, having a capacity sufi'icient to pass the entire volume of air thrown by the blower 3I, through the fitting 33, conduit 35, port 41, chamber 2I, and tube I6 to the coal room I3. This passage being open, no pressure can build up in the passage 32 and box I2, and no air will be pushed through the barrier comprising the fuel bed, into the combustion chamber. Thus, whether coal feed screws I1 and 21 are loaded or empty, because of the large capacity of air scoop 33 in the direct path of the maximum blower wheel pressure and the ample capacity of conduit 35, air is always delivered to chamber 2I in greater pressure than the resulting static pressure in air box I2. Therefore, under all condi tions the pressure existing in chamber 2I will exceed the pressure in the combustion chamber. Thus I provide a higher pressure air cushion at chamber 2I which positively prevents any flow of smoke from the combustion chamber back through the conduit 25; and, when the tube I6 is empty or substantially so, there is automatically provided an unrestricted air-flow passage through which the entire volume of air handled by the blower may escape to atmosphere, thus robbing the combustion chamber of the air normally supplied thereto, reducing the static pressure normally existing therein, and tending to cause extinguishment of the fire therein.

I claim as my invention:

1. For use with a source of supply of solid fuel in communication with atmosphere and a furnace having a combustion chamber, conveyor means including a closed passage connecting said source and said chamber and means in said passage operable to transport fuel from such source through said passage to such chamber and to build and maintain a fuel bed in such chamber, a blower having an outlet, conduit means connecting said blower outlet with said combustion chamber through such fuel bed, and other conduit means having a relatively large mouth located in said outlet and masking at least onethird of the effective area of said first-named conduit means, said other conduit means establishing communication between the outlet of said blower and said closed passage intermediate the ends thereof to establish and maintain insaid passage a static pressure higher than that existing in said chamber.

2. The organization of claim 1 in which said last-named conduit means discharges into: said passage in a direction substantially transverse to the direction of flow of fuel through said passage.

3. Stoker mechanism comprising a closed-tube screw conveyor having an open end adapted to be embedded in a supply ofsolid' fuel, a transfer box entered by the opposite end'of' said conveyor, a second closed-tube screw conveyor having one end mounted insaid box to receive f'uel from said first conveyor and adapted to have its opposite end operatively connected to supply fuel to a combustion chamber which is provided with a vent, a blower having an outlet, means for driving said conveyors and said blower, means providing a passage for conducting air from said blower and adapted to be connected to deliver such air-to a region in such combustion chamber which separated from such vent by thereg-ion to which fuel is supplied by said second conveyor, and other means establishing apassage for conducting air from said blower to said transfer box; said lastnamed passage communicating with said blower outlet in the region of maximum blower delivery pressure, masking at least one-third of the effective area of said first-named passage, and having a capacity sufiicient topass substantially the entire volume of air delivered by-saidblower, whereby, when the tube of said first-named conveyor is substantially empty offuel, substantially the full volume of air delivered by said blower will be exhausted to atmosphere through the tube of said first-named conveyor, thus'reducing the air pressure in the regionbelow the combustionchamber;

and, when the tube of said second conveyor is substantially empty of fuel, air will flow from said transfer box through the tube of said second conveyor to said combustion chamber in a region on that side of the region to which fuel is supplied adjacent said vent, thus preventing gas flow from said combustion chamber through the tube of said second conveyor toward said transfer box.

4. In a solid fuelstoker including a fuel-feeding conduit and means for moving fuel through saidconduit to a combustion chamber, a blower having an outlet, conduit means connecting said blower to supply a combustion-supporting gas to such combustion chamber, and conduit means having a capacity sufi'icient to pass substantially the entire volume of gas delivered by said blower when said fuel conduit is substantially empty of coal, said last-named conduit means communieating with said blower outlet at the point of maximum blower delivery pressure and masking at least one-third of the effective area of said first-named conduit means and connecting said blower outlet to said fuel-feeding conduit adjacent the inlet end thereof to establish and maintain in said fuel-feeding conduit a fluid pressure exceeding the fluid pressure in said combustion chamber.

DAVID T. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,844,026 Banfield Feb; 9, 1932 1,844,042 Parker et a1 Feb. 9, 1932 1,954,856 Wetmore Apr. 1'7, 1934 2,191,219 Peltz' Feb. 20, 1940 2,234,959 Brice Mar. 18, 1941 2,364,166 Scholl Dec. 5-, 1944 2,365,679 Casey Dec. 26, 1944 2,378,805 Spicer et a1 June 19,1945 

